Modern aircrafts comprise one or more control systems. These control systems notably perform functions for guiding the aircraft, for management of its flight path, for management of the alarms, for management of the maintenance, etc. These control systems generally comprise one or more computers communicating with each other via an onboard communications network. Conventionally, one computer can be dedicated to one particular function. In the recent aircraft, these computers may be replaced, at least in part, by modular avionics computers of the IMA (Integrated Modular Avionics) type. Each IMA computer can host several applications corresponding to functions conventionally implemented by separate dedicated computers. The various computers, whether they be of the dedicated or IMA type, generally take the form of a rack accommodating several electronics boards connected to a bus of the back-plane type. Several computers of an aircraft are generally assembled in electronics cabinets, in an area of the aircraft commonly referred to as the “electronics bay”, these computers being connected to an onboard communications network in such a manner as to be able to exchange information between them and/or with other computers of the aircraft. Each computer corresponds to a subscriber to said communications network. Each computer may for example be connected to a switch of a deterministic full-duplex Ethernet communications network, such as for example an AFDX® data network. Other embodiments may be envisioned, for example a communications network of the ring type. The various computers, whether they be of the dedicated or IMA type, are commonly referred to as LRU (Line Replacement Unit), because, in the case of a failure, the rack corresponding to a computer must be removed from the aircraft, since an electronics board cannot be removed from the rack and replaced onboard the aircraft during the operation of the computer.
In modern aircrafts, the LRU computers may be replaced by electronics enclosures. The principle of an enclosure is to assemble, within the same rack, electronics boards each supporting functionalities usually supported by an LRU. These electronics boards share common resources, such as for example an electrical power supply, a switch of a communications network, etc. These resources are generally supported by other electronics boards integrated into the rack, for example an electrical power supply board, a communications network switch board, etc. The various electronics boards of an enclosure are referred to as LRM (Line Replacement Module), because it is possible to replace a board of an enclosure without interrupting the operation of the latter. The various LRMs of an enclosure generally communicate with one another via a communications network, in particular by means of an aforementioned switch. The various electronics enclosures of an aircraft are generally integrated into the avionics bay.
In the case of a communications network connecting together several subscribers to this communications network, these subscribers corresponding in particular to LRUs or to LRMs and the network comprising a switch, a failure of the switch can lead to the impossibility of communicating for all of the computers connected to this switch. In order to pre-empt this eventuality, a redundancy of the switches is generally provided in an onboard communications network. In the case of a communications network of the ring type, if a computer subscriber to this communications network crashes, this can lead to an interruption of the communications between the other computer subscribers to the network.